Multiwell plates have existed for many years. Most are in multiples of 6, 8 or 12 such as 24, 96 or 384 wells in a single plate.
Methods to attach the filter material to the bottom of the plate so as to seal off the bottom of each well by the porous filter material have included mechanical means such as friction fitting of individual pieces in each well or clips or edge bands to hold the filter material against the bottom; adhesives, heat bonding, over molding and thermal bonding via an under drain.
Each approach has its drawbacks. Simply stuffing a cut piece into each well is time consuming and provides less than 100% sealing accuracy. With the 384 well format, this approach is impractical. Likewise, using a clamp or edge band allows the filter material in the middle to separate from the bottom of the wells allowing for cross talk or contamination between wells.
Adhesives require proper placement and alignment of the adhesive and filter material so as to prevent adhesives from spreading into the area of filter inside the well that reduces its active filtration area. Moreover, adhesives do not extend through the entire thickness of the filter material allowing for cross talk and contamination between wells through the filter material beyond the glue.
Overmolding or insert molding eliminates cross talk and forms an integral well, but it is costly to set up and run and is a relatively slow process. Moreover, its use at smaller well sizes (384+) is limited by the ability to form channels and gates for the introduction of the molten plastic in that small area.
Using thermal energy to bond and seal the filter to the bottom of the plate is difficult. Achieving 100% sealing of the filter to the bottom by thermal bonding is not possible. Some filter materials do not bond properly to the material of the plate, limiting this approach to only compatible materials. Other filters are extremely heat sensitive making this approach untenable as the filter structure tends to collapse to such an extent that active filtration area is compromised.
Using thermal energy to trap the filter between an upper plate and lower plate is possible. Again, it is limited in speed and cost to set up and run. Moreover, it requires the use of a fixed design for a bottom plate that may either be unnecessary or improperly suited for the desired application.
What is desired is a process that is fast, inexpensive and reliable for making a multiwell filtration plate where each well is integrally sealed about its edge and no cross talk or contamination between wells is possible. The present invention provides such a process.